Passive device cell and fabrication process thereof

ABSTRACT

An embodiment of the invention provides a passive device cell. The passive device cell has a substrate layer, a passive device, and an intermediary layer formed between the substrate layer and the passive device. The intermediary layer includes a plurality of LC resonators.

BACKGROUND

1. Technical Field

The invention relates generally to a passive device, and moreparticularly, to a passive device that is separated from a substratelayer by an intermediary layer.

2. Related Art

Passive devices are circuit components that are incapable of generatingpower gain; in other words, they cannot amplify signals. Capacitors,inductors, and resistors are some well-known examples of passivedevices. Generally speaking, in an integrated circuit (IC), passivedevices are formed on a layer above the substrate. When the currentflowing through a passive device is changing, the time-varying currentwill induce eddy currents in the underneath substrate, causing someenergy to be wasted. The energy waste may deteriorate the passivedevice's performance.

SUMMARY

The invention provides embodiments that may enhance a passive device'performance and make the fabrication process thereof more robust.

An embodiment of the invention provides a passive device cell. Thepassive device cell has a substrate layer, a passive device, and anintermediary layer formed between the substrate layer and the passivedevice. The intermediary layer includes a plurality of LC resonators.

Another embodiment of the invention provides a passive device cell. Thepassive device cell has a substrate layer, a passive device, and ametamaterial layer formed between the substrate layer and the passivedevice.

Still another embodiment of the invention provides a passive devicefabrication process. The process includes a step of forming anintermediary layer above a substrate layer and a step of forming apassive device above the intermediary layer. The intermediary layerincludes a plurality of LC resonators.

Other features of the invention will be apparent from the accompanyingdrawings and from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is fully illustrated by the subsequent detaileddescription and the accompanying drawings, in which like referencesindicate similar elements.

FIG. 1 shows an exemplary cross-sectional view of a passive device cellin an IC according to an embodiment of the invention.

FIG. 2 and FIG. 3 show two exemplary top views of the passive devicecell depicted in FIG. 1.

FIG. 4 shows an exemplary equivalent circuit of an LC resonator.

FIG. 5 shows an exemplary top view of an LC resonator embodied by asplit-ring resonator.

FIG. 6 and FIG. 7 show two other exemplary top views of the passivedevice cell depicted in FIG. 1.

FIG. 8 shows a simplified flowchart of a process for fabricating thepassive device cell of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary cross-sectional view of a passive device cell110 of an IC 100 according to an embodiment of the invention. The IC 100may include both passive devices and active devices, or include passivedevices but not active devices. If it does not include active devices,the IC 100 may be referred to as an integrated passive device (IPD).

The IC 100 has at least three layers, including a circuit componentlayer 120, an intermediary layer 140, and a substrate layer 160. Theintermediary layer 140 lies between the circuit component layer 120 andthe substrate layer 160. Each of these layers may have one or multiplesub-layers. The circuit component layer 120 and the substrate layer 160may stretch throughout the whole IC 100. The intermediary layer 140 maystretch throughout the whole IC 100 or stretch in the IC 100 to whereverpassive devices are formed above.

The passive device cell 110 is a part of the IC 100 used to form apassive device 122. Specifically, in the part of the circuit componentlayer 120 within the cell 110, the passive device 122 is formed. Becausethe passive device 122 may be a resistor, a capacitor, an inductor, oranother kind of passive device, FIG. 1 only uses a rectangle torepresent the cross-sectional view of the passive device 122. Other areain the circuit component layer 120 shown in FIG. 1 but not occupied bythe passive device 122 may have been worn down or etched out.

The intermediary layer 140 may be a metamaterial layer, which may alsobe referred to as a negative index material layer or a left-handedmedium layer. FIG. 2 and FIG. 3 shows exemplary top views of the passivedevice cell 110 of FIG. 1. The passive device 122 shown in theseexamples is an inductor. Furthermore, each of small solid rectanglesrepresents an LC resonator formed in the intermediary layer 140. Toavoid distraction, only one of the LC resonators is indexed as 142;other not indexed LC resonators may also be referred to as LC resonators142.

As FIG. 2 and FIG. 3 indicate, the intermediary layer 140 is a layer inwhich LC resonators 142 are formed. Specifically, beneath each passivedevice (such as the passive device 122) formed in the circuit componentlayer 120, there may be a plurality of LC resonators 142 formed in theintermediary layer 140. In the example shown in FIG. 2, the LCresonators 142 constitute a two dimensional array in the intermediarylayer 140. In the example shown in FIG. 3, the LC resonators 142 do notconstitute a uniform array in the intermediary layer 140 but arearranged less regularly.

The area occupied by the LC resonators 142 may be larger than, equal to,or smaller than, the area occupied by the above passive device 122. TheLC resonators 142 may be on a plane substantially parallel to the threelayers 120, 140, and 160. Depending on the size of the passive device122 and the sizes of the LC resonators 142, the LC resonators 142beneath the passive device 122 may have hundreds or even thousands ormember resonators. The optimal size and configuration of the LCresonators 142 may be determined through electromagnetic (EM)simulation. As an example, each of the LC resonators 142 is more than100 times smaller than the passive device 122.

Each LC resonator 142 may have an equivalent circuit that includes atleast an equivalent inductor and an equivalent capacitor connected inparallel. An example of such an equivalent circuit is depicted in FIG.4. To make the LC resonator 142 equivalent to the circuit depicted inFIG. 4, the LC resonator 142 may have at least a pair of conductivecomponents, such as a pair of metal segments, adjacent to andelectrically isolated from each other.

For example, each LC resonator 142 may be a split-ring resonator (SRR).The SRR may include at least a pair of conductive split-rings. The twosplits of the pair of conductive split-rings may face two differentdirections (e.g. two opposite directions). If the two conductivesplit-rings are on a same plane, one of them may be substantiallyencircled by the other. But for its split, each of the conductivesplit-rings may resemble a circle, a rectangle, or another geometricfigure. FIG. 5 shows an exemplary top view of an LC resonator 142embodied by an SRR. This LC resonator 142 has a first conductivesplit-ring 142 a and a second conductive split-ring 142 b. The twoconductive split-rings 142 a and 142 b both resemble letter “C” but facetwo opposite directions. The second conductive split-ring 142 b issubstantially encircled by the first conductive split-ring 142 a.

FIG. 6 and FIG. 7 show two other exemplary top view of the passivedevice cell 110 of FIG. 1. Unlike the examples shown in FIG. 2 and FIG.3, in these two examples the intermediary layer 140 is formed with notonly LC resonators 142 but also pairs of dashed conductive lines. Eachof the dashes forming these dashed lines may be a metal segment isolatedfrom other metal segments. To avoid distraction, only a pair of dashedconductive lines is indexed in each of FIG. 6 and FIG. 7; the indexedlines include a first dashed conductive line 146 a and a second dashedconductive line 146 b. Each pair of dashed conductive line not labeledin FIG. 6 or FIG. 7 may also be referred to as dashed conductive lines146 a and 146 b. The first dashed conductive line 146 a and the seconddashed conductive line 146 b are beside and substantially parallel toeach other. Furthermore, in these examples, the gaps between the firstdashed conductive line 146 a are not aligned with the gaps between thesecond dashed conductive line 146 b. The pair of dashed conductive lines146 a and 146 b may be equivalent to plenty of tiny LC resonators.

In the example shown in FIG. 6, the LC resonators 142 constitute a twodimensional array in the intermediary layer 140. In the example shown inFIG. 7, the LC resonators 142 do not constitute a uniform array in theintermediary layer 140; instead, the LC resonators 142 and dashedconductive lines 146 a and 146 b are arranged less regularly in FIG. 7.Although each pair of dashed conductive lines 146 a and 146 b may bestraight lines, they may also be curved lines that are parallel to eachother.

FIG. 8 shows a simplified flowchart of a process for fabricating thepassive device cell 110. This figure depicts only the steps directlyrelated to the understanding of the invention. Each of the stepsdepicted in FIG. 8 may include multiple sub-steps. First, at step 820,the intermediary layer 140 is formed above the substrate layer 160.Specifically, this step may involve the doping or deposition ofconductive material onto a semiconductor wafer to form the conductivepatterns described above. Then, at step 840, the passive device 122 isformed above the intermediary layer 140. Step 840 may be performedstably because the intermediary layer 140, which is relatively moresolid, is underneath the passive device 122.

The inclusion of the intermediary layer 140 between the passive device122 and the substrate layer 160 may have several advantages. First, thismay enhance the passive device 122's performance. For example, wheneverthe current flowing through the passive device 122 is changing, thistime-varying current may induce magnetic field lines around the passivedevice 122. The LC resonators in the intermediary layer 140 may serve astiny LC tanks and prevent some of the magnetic field lines from enteringthe part of the substrate layer 160 underneath the passive device 122.As to the pairs of dashed conductive lines depicted in FIG. 6 and FIG.7, they may enhance the blockage of magnetic field lines, especially inthe direction depicted in the figures. Therefore, the intermediary layer140 may decrease the amount of eddy currents induced in the part of thesubstrate layer 160 and as a result reduce energy waste. With lessenergy wasted, the passive device 122 may have an enhanced performanceQ.

Second, the repetitive patterns in the intermediary layer 140 may makethe foundations underneath the passive device 122 more rigid. Even ifsome parts of the circuit component layer 120 have been worn down oretched out, the revealed upper surface of the intermediary layer 140 maystill be relatively flat. This means that the inclusion the intermediarylayer 140 may make the fabrication processes, especially thechemical-mechanical polishing (CMP) process, of the IC 100 more robust.Third, the intermediary layer 140 may make it unnecessary to usehigh-resistance (HR) substrate, pattern ground shielding (PGS), or thickmetal for reducing eddy currents, and hence may cut down on the overallfabrication costs. Fourth, when being compared with PGS, the tinyrepetitive patterns in the intermediary layer 140 may have relativelysmaller parasitic capacitances.

In the foregoing detailed description, the invention has been describedwith reference to specific exemplary embodiments thereof It will beevident that various modifications may be made thereto without departingfrom the spirit and scope of the invention as set forth in the followingclaims. The detailed description and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

What is claimed is:
 1. A passive device cell, comprising: a substratelayer; an intermediary layer formed above the substrate layer, theintermediary layer comprising a plurality of LC resonators; and apassive device formed above the intermediary layer, wherein the size ofeach of the plurality of LC resonators is more than 100 times smallerthan the size of the passive device.
 2. The passive device cell of claim1, wherein the plurality of LC resonators constitute a two dimensionalarray in the intermediary layer.
 3. The passive device cell of claim 1,wherein each of the plurality of LC resonators comprises a pair ofconductive components adjacent to and electrically isolated from eachother.
 4. The passive device cell of claim 3, wherein the pair ofconductive components of each of the plurality of LC resonators are apair of conductive split-rings, each of the conductive split-rings has asplit, the two splits of the respective pair of conductive split-ringsface two opposite directions, and one of the respective pair ofconductive split-rings is substantially encircled by the other.
 5. Thepassive device cell of claim 1, wherein the intermediary layer furthercomprises a plurality of pairs of segmented conductive lines, each ofthe plurality of pairs of segmented conductive lines comprises a firstsegmented conductive line and a second segmented conductive line besideand substantially parallel to each other, and gaps between the firstsegmented conductive line are not aligned with gaps between the secondsegmented conductive line.
 6. A passive device cell, comprising: asubstrate layer; a metamaterial layer formed above the substrate layer,the metamaterial layer comprising a plurality of LC resonators; and apassive device formed above the metamaterial layer, wherein the size ofeach of the plurality of LC resonators is more than 100 times smallerthan the size of the passive device.
 7. The passive device cell of claim6, wherein the plurality of LC resonators constitute a two dimensionalarray in the metamaterial layer.
 8. The passive device cell of claim 6,wherein the metamaterial layer further comprises a plurality of pairs ofsegmented conductive lines, each of the plurality of pairs of segmentedconductive lines comprises a first segmented conductive line and asecond segmented conductive line beside and substantially parallel toeach other, and gaps between the first segmented conductive line are notaligned with gaps between the second segmented conductive line.
 9. Thepassive device cell of claim 6, wherein each of the plurality of LCresonators is a split-ring resonator.
 10. The passive device cell ofclaim 9, wherein the split-ring resonator of each of the plurality of LCresonators comprises a pair of conductive split-rings, and each of theconductive split-rings has a split.
 11. The passive device cell of claim10, wherein the two splits of the respective pair of conductivesplit-rings face two opposite directions, and one of the respective pairof conductive split-rings is substantially encircled by the other.
 12. Apassive device fabrication process, comprising: forming an intermediarylayer above a substrate layer, the intermediary layer comprising aplurality of LC resonators; and forming a passive device above theintermediary layer, wherein the size of each of the plurality of LCresonators is more than 100 times smaller than the size of the passivedevice.
 13. The process of claim 12, wherein each of the plurality of LCresonators comprises a pair of conductive components adjacent to andelectrically isolated from each other.
 14. The process of claim 13,wherein the pair of conductive components of each of the plurality of LCresonators are a pair of conductive split-rings, each of the conductivesplit-rings has a split, the two splits of the respective pair ofconductive split-rings face two opposite directions, and one of therespective pair of conductive split-rings is substantially encircled bythe other.
 15. The process of claim 12, wherein the intermediary layerfurther comprises a plurality of pairs of segmented conductive lines,each of the plurality of pairs of segmented conductive lines comprises afirst segmented conductive line and a second segmented conductive linebeside and substantially parallel to each other, and gaps between thefirst segmented conductive line are not aligned with gaps between thesecond segmented conductive line.
 16. The process of claim 12, whereinthe plurality of LC resonators constitute a two dimensional array in theintermediary layer.